Horses carrying out low level exercise generally lose 5 to 10 liters of sweat per hour. Horses working at high intensities can lose as much as 15 liters of sweat per hour.

Photo: Anne M. Eberhardt/The Horse

Editor's note: This article is part of TheHorse.com's ongoing coverage of topics presented at the 2012 Kentucky Equine Research Conference, held May 17-18 in Lexington, Ky.

Many performance horse owners supplement their charges' feed with electrolyte supplements, especially during the hot summer months. As one researcher explained at the 2012 Kentucky Equine Research (KER) Conference, held May 17-18 in Lexington, Ky., providing performance horses with electrolytes--especially in the hot summer months--is crucial to maintaining top performance and healthy animals.

Salix and Electrolytes

About 90% of Thoroughbred racehorses and 70% of Standardbred racehorses in the United States are treated with furosemide (commonly known as Salix) in an attempt to reduce or eliminate the effects of exercise-induced pulmonary hemorrhage, said Joe Pagan, PhD, president of Kentucky Equine Research (KER). Because furosemide creates a diuretic effect in horses by reducing the reabsorption of sodium into the kidneys, a team of researchers at KER evaluated the drug's effect on the equine electrolyte balance; they found that:

Essentially, Pagan's team found that furosemide has a significant negative effect on electrolyte balances in horses.

"Longer-term studies are needed to assess the effect of chronic furosemide administration on calcium loss and skeletal soundness in horses," he said. "Additional studies are also needed to develop electrolyte supplement strategies to correct the electrolyte imbalances caused by furosemide administration in racehorses."

--Erica Larson

"Electrolytes are a critical component of a performance horse's feeding program because they play an important role in maintaining osmotic pressure, fluid balance, and nerve and muscle activity," explained Joe Pagan, PhD, president of KER in Versailles, Ky.

He relayed that losses of sodium, potassium, and chloride in sweat can cause muscle fatigue and weakness and decrease the horse's thirst response to dehydration. Thus, he said, it's important for performance horses to start an intense workout or competition with adequate electrolyte and hydration levels to prevent excessive electrolyte loss through sweat.

Pagan explained that horses carrying out low level exercise generally lose 5 to 10 liters of sweat per hour, depending upon a number of factors including duration and intensity of exercise, ambient temperature, and humidity. Horses working at high intensities can lose as much as 15 liters of sweat per hour, he noted.

Fulfilling Electrolyte Needs

So how can we ensure our horses are consuming enough potassium, sodium, and chloride to maintain adequate electrolyte levels? Pagan noted that simply evaluating a horse's feed is a good place to start.

"Unfortified hay and grain rations tend to be deficient in sodium and contain variable quantities of chloride," he said. "In contrast, most forage is high in potassium and when fed in adequate quantities will meet daily potassium requirements."

For horses in light work or idle horses, Pagan recommended supplying a free choice salt block or topdressing salt (one to two ounces per day for idle horses) on daily grain or concentrate rations.

Horses in moderate to heavy work or horses losing large amounts of sweat due to high temperatures will likely necessitate additional electrolyte supplementation.

"Horse owners need to look for electrolytes that are high in sodium, chloride, and to a lesser extent potassium," Pagan said. "Care should be used in adding electrolytes to a horse's water as it may decrease water intake. If adding electrolytes to water, make sure a second source of straight water is available."

Pagan cautioned that some commercially available electrolyte supplements contain sugar (called dextrose on the ingredient list), which is meant to "improve electrolyte uptake." He described recent research carried out at KER, however, that showed that adding dextrose to electrolytes had no impact on the rate or duration of increased electrolyte levels. A second study showed no difference in the rate of water uptake from the digestive tract when comparing electrolytes with and without dextrose.

Researchers are also looking into the potential of "encapsulated sodium bicarbonate designed to prevent hindgut acidosis in horses," Pagan said. He relayed that research conducted at KER showed the sodium bicarbonate is digested similarly to the sodium in electrolytes, but more slowly, which leads to greater sodium retention. More research is needed on the product's use in an electrolyte fashion, he noted.

Take-Home Message

Electrolyte supplementation can help increase performance in sport horses when provided in conjunction with good quality forage and a balanced diet. For lightly exercised horses, adding a free choice salt block to the diet or topdressing the animal's rations with salt should supply adequate amounts of electrolytes.

About the Author

Erica Larson, news editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in eventing with her OTTB, Dorado.

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